Refrigerating apparatus and inverter device

ABSTRACT

A refrigerating apparatus having a refrigerating cycle that comprises a compressor, an electric motor that drives the compressor, and an inverter device that variably controls the operating frequency of the electric motor. The inverter device includes a converter circuit that converts an A.C. voltage from an A.C. power supply into a D.C. current, an inverter circuit comprising a D.C./A.C converter, and a shunt resistance that detects a D.C. current flowing through a switching element of the inverter circuit. The shunt resistance detects a D.C. current, and the detected D.C. current value is calculated as a sine wave A.C. current for the electric motor in relation to action of the switching element.

BACKGROUND OF THE INVENTION

The present invention relates to a refrigerating apparatus including a variable speed motor for compressor, and an inverter device to be used in the apparatus.

Conventionally, in order to achieve miniaturization and to enhance a refrigerating cycle in reliability in a refrigerating apparatus and an inverter device to be used in the apparatus, it is known and described in, for example, JP-A-2003-289675 that a substrate with a power semiconductor and a microcomputer mounted thereon is enclosed by a box-shaped case and arranged in a layered manner with a connector substrate for interface disposed topmost.

In the conventional art described above, since a current sensor (current detection mechanism) for detecting an electric current fed to an electric motor is used, a large mount area is needed. That is, the current sensor is a high function part to take in a current output to a motor once, to grasp magnetic flux generated by the flowing current, to effect voltage conversion and to output to a control substrate, and so the part itself is large to become obstacles in miniaturization of the whole.

Also, in refrigerating apparatuses (air conditioners, refrigerating machines), an electric motor relatively consumes a large electric power and is in many cases driven by a three-phase electric source. For inverter control, at least two phases (for example, U-phase and V-phase among three-phase output (U-phase, V-phase and W-phase)) of the current to be output to the electric motor must be detected, and to provide a space for detection is disadvantageous to miniaturization and enhancement in reliability.

It is an object of the present invention to make an inverter device small in size and particularly thin in keeping with miniaturization in air conditioners and refrigerating apparatuses such as refrigerating machines, in particular, outdoor devices and to achieve enhancement in reliability for suitability to fault diagnosis.

BRIEF SUMMARY OF THE INVENTION

In order to attain the object, the invention provides a refrigerating apparatus having a refrigerating cycle that includes a compressor which is driven by an electric motor, of which operating frequency is variably controlled by an inverter device, wherein the inverter device includes a converter circuit that converts an A.C. voltage from an A.C. power supply into a D.C. current, an inverter circuit comprising a D.C./A.C converter, and a shunt resistance that detects a D.C. current flowing through a switching element of the inverter circuit, and a D.C. value detected by the shunt resistance is calculated as a sine wave A.C. current for the electric motor in relation to action of the switching element.

Also, desirably, the inverter device comprises a first substrate on a surface of which the shunt resistance is mounted and on an opposite surface of which radiating fins are closely attached; a second substrate on which a microcomputer that controls the switching element, a current detection circuit that processes a detection value detected by the shunt resistance, a driver circuit that causes the switching element to perform a switching operation, a connector for communication circuit/interface that communicates with a high-order control substrate, and a power circuit that supplies control power to the microcomputer, the current detection circuit, the driver circuit, and the communication circuit, are mounted; and a case that covers sides of the first substrate, the case being provided with terminal blocks for electric power input and motor output; the first substrate and the second substrate are arranged in the order of the first substrate and the second substrate in a layered manner from a bottom surface of the case, the first substrate and the second substrate are connected to each other by a lead pin, and gel is filled on a surface of the first substrate on which a power semiconductor is mounted.

It is preferable that the operating frequency be output to the high-order control substrate via the connector for interface.

Further, it is preferable that refrigerating cycle information (temperature, pressure, opening degrees of expansion valves, rotating speeds of fans) be input into the microcomputer via the connector for interface, and the refrigerating cycle be controlled by the microcomputer.

Further, it is preferable that a nonvolatile memory be arranged on the second substrate and data of detection gain of the shunt resistance be stored and retained in the nonvolatile memory.

Further, it is preferable that the refrigerating apparatus further comprise an active switching element that constitutes an active circuit, and a shunt resistance that detects an electric current of a single-phase power supply input, and a single-phase power supply be input into the converter circuit.

Also, the invention provides an inverter device that variably controls the operating frequency of an electric motor, the inverter device comprising a converter circuit that converts an A.C. voltage from an A.C. power supply into a D.C. current, an inverter circuit comprising a D.C./A.C converter, and a shunt resistance that detects a D.C. current flowing through a switching element of the inverter circuit, wherein a D.C. value detected by the shunt resistance is calculated as a sine wave A.C. current for the electric motor in relation to action of the switching element.

Further, desirably, the inverter device further comprises: a first substrate on a surface of which the shunt resistance is mounted and on an opposite surface of which radiating fins are closely attached; a second substrate on which a microcomputer that controls the switching element, a current detection circuit that processes a detection value detected by the shunt resistance, a driver circuit that causes the switching element to perform a switching operation, a connector for communication circuit/interface that communicates with a high-order control substrate, and a power circuit that supplies control power to the microcomputer, the current detection circuit, the driver circuit, and the communication circuit, are mounted; and a case that covers sides of the first substrate, the case being provided with terminal blocks for electric power input and motor output, the first substrate and the second substrate are arranged in the order of the first substrate and the second substrate in a layered manner from a bottom surface of the case, the first substrate and the second substrate are connected to each other by a lead pin, and gel is filled on a surface of the first substrate on which a power semiconductor is mounted.

Further, it is preferable that the second substrate be provided with a frequency change-over mechanism capable of changing and fixing the operating frequency of the compressor.

Further, it is preferable that a nonvolatile memory be arranged on the second substrate and data of detection gain of the shunt resistance are stored and retained in the nonvolatile memory.

Further, it is preferable that a single-phase power supply be input into the converter circuit, and an active switching element that constitutes an active circuit, and a shunt resistance that detects an electric current of a single-phase power supply input be provided.

According to the invention, the shunt resistance for overcurrent protection of the inverter power semiconductor is substituted for current detection means for inverter control, so that it is possible to make, in particular, the inverter device thin and to further achieve an enhancement in reliability.

Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a view showing a refrigerating cycle of a refrigerating apparatus according to an embodiment of the invention.

FIG. 2 is a block diagram of an inverter device according to an embodiment of the invention.

FIG. 3 is a perspective view showing assembling way of an inverter device according to an embodiment of the invention.

FIG. 4 is a perspective view showing a state, in which an inverter device according to an embodiment of the invention is assembled.

FIG. 5A is a cross sectional view showing an inverter device according to an embodiment of the invention.

FIG. 5B is a cross sectional view showing an inverter device according to an embodiment of the invention.

FIG. 6 is a view illustrating current detection means according to an embodiment of the invention.

FIG. 7 is a view illustrating current reproduction means according to an embodiment of the invention.

FIG. 8 is a block diagram of a single-phase inverter device according to a further embodiment of the invention.

FIG. 9 is a perspective view showing assembling way according to a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

When a motor output current can be grasped by a shunt resistance for overcurrent protection as far as further miniaturization of an inverter device is concerned in keeping with miniaturization in air conditioners, refrigerating apparatuses such as refrigerating machines, etc. and in particular, an outdoor unit, it is possible to eliminate a current sensor, to make a control substrate small in size, and to integrate functions of substrates in the inverter device to reduce the number of substrates.

An embodiment of the invention will be described below with reference to the drawings.

FIG. 1 is a system drawing showing a refrigerating cycle of a refrigerating apparatus according to an embodiment of the invention, in which a compressor 101, an indoor heat exchanger 102, an indoor expansion valve 104, an outdoor heat exchanger 105, and an accumulator 107 are successively connected to circulate a refrigerant therethrough to form a refrigerating cycle. When a room is cooled, a refrigerant compressed by the compressor 101 is condensed and liquefied in the outdoor heat exchanger 105, thereafter reduced in pressure by the indoor expansion valve 104, evaporated by the indoor heat exchanger 102, and returned to the compressor 101. An indoor fan 103 expedites heat exchange in an indoor unit 109 and an outdoor fan 106 expedites heat exchange in an outdoor unit 108.

The compressor 101 is driven by an electric motor 111, of which operating frequency is variably controlled in relation to the capacity required for the refrigerating cycle, and the operating frequency is controlled by an inverter device 210.

In the refrigerating cycle, an opening degree of the indoor expansion valve 104, or an outdoor expansion valve (not shown), which serves to regulate the flow rate of the refrigerant, rotating speeds of the indoor fan 103 and the outdoor fan 106, a four-way valve (not shown) that switches over operating modes of cooling/heating, and the like, other than the rotating speed of the compressor 101 are controlled. An operation command signal issued by a remote controller that performs setting of an operating mode and temperature, temperature (discharged-gas temperature of the compressor, outside air temperature, heat-exchanger temperature, evaporating temperature, suction temperature, blow off temperature, freezing point, gas-pipe temperature, etc.) signals, and pressure (suction pressure and discharge pressure of the compressor) signals, etc. are input as information for the control into a cycle control substrate 254.

Also, an inverter demand frequency output from the cycle control substrate 254 is input via an interface connector 242, and an operating frequency and a motor operating current are output to the cycle control substrate 254 from the inverter device 210.

Refrigerating-cycle control is provided by inputting a detection signal and a command signal, which have been input into the cycle control substrate 254, into a microcomputer 231 via the interface connector 242. The inverter device 210 can control various control mechanisms (the outdoor expansion valve, the outdoor fan 106, the four-way valve to switch over the operating modes of cooling/heating), and the control circuit for the whole refrigerating cycle is simplified to be reduced in wiring, etc. and made small in size.

FIG. 2 shows a block diagram of the inverter device. The inverter device 210 comprises a first substrate (metallic substrate) 220 and a second substrate (control substrate) 230. On the first substrate 220, a converter 222 a including rectifying devices 222 and serving to convert an A.C. voltage from an A.C. power supply 250 into a D.C. current, an inverter 221 a including switching elements 221 and comprising a D.C./A.C converter to constitute an inverter power semiconductor, and a shunt resistance 225 to detect a D.C. current flowing through the switching elements 221 are mounted. Further, radiating fins made of copper or aluminum are attached closely to an opposite surface to the mount surface. On the second substrate 230, mounted are the microcomputer 231, a current detection circuit 234 that processes a detection value detected by the shunt resistance 225, a driver circuit 232 that causes the inverter power semiconductor to perform a switching operation, a communication circuit 241 that communicates with the cycle control substrate 254, and a power circuit 233 that supplies control power to the microcomputer 231, the current detection circuit 234, the driver circuit 232, and the communication circuit 241.

An A.C. voltage from the A.C. power supply 250 is converted by the converter 222 a (in which a plurality of rectifying devices 222 are bridge-connected) into D.C. current, and the inverter 221 a (power conversion means, in which the switching elements 221 are three-phase bridge-connected) being a D.C./A.C converter is subjected to A.C. frequency control by the microcomputer 231 to drive the electric motor 111.

The A.C. voltage is rectified by the plurality of rectifying devices 222 in the converter 222 a to be conducted to a smoothing capacitor 251 via a magnet switch 253 that operates or stops the compressor 101, and a power factor improvement reactor 252.

Also, a rush inhibition resistance 244 is provided in parallel to the magnet switch 253 so as to prevent the magnet switch 253, which closes at the time of power-on, from being fused by an excessive rush current that flows through the capacitor 251.

In the inverter 221 a, flywheel elements 223 are provided in parallel to the switching elements 221 and mounted together to the first substrate 220 in order to regenerate that counter-electromotive force from the electric motor 111, which is generated when the switching elements 221 are switched.

An electric current supplied to the electric motor 111 is detected as D.C. current, which is to flow to the inverter power semiconductor, by the shunt resistance 225, amplified by the current detection circuit 234 to be taken into the microcomputer 231, and calculated and reproduced as sine wave A.C. current, which is being output to the electric motor, by the microcomputer 231 to be monitored or controlled.

The driver circuit 232 is provided between the microcomputer 231 and the switching elements 221 to amplify a weak signal from the microcomputer 231, to a level, in which the switching elements 221 can be driven.

The communication circuit 241 comprises the interface connector 242, into which a signal from the cycle control substrate 254 is input, and a photo-coupler 243 that transmits an input signal as an optical signal to the microcomputer 231, and the communication circuit makes transmission and reception in a state, in which electric isolation is established.

A part of D.C. current generated by the converter 222 a on the first substrate 220 is regulated to a control power of 5 V or 15 V or so from high voltage used in the inverter 221 a, by the power circuit 233 provided on the second substrate 230 to be supplied to the microcomputer 231, the current detection circuit 234, the driver circuit 232, and the communication circuit 241.

Also, by providing a frequency change-over switch 235, capable of changing and fixing the operating frequency of the compressor, on the second substrate (control substrate) 230, performance evaluation on the operating frequency is made possible.

Further, a nonvolatile memory 236 is arranged on the second substrate (control substrate) 230, and data of detection gain (an inclination of a straight line that connects a detection value taken into the microcomputer 231 via the current detection circuit 234 when a predetermined electric current is caused to flow through the shunt resistance 225, and a detection value taken into the microcomputer 231 in a state, in which no electric current flows through the shunt resistance 225) in the case where the shunt resistance 225 is mounted on the first substrate (metallic substrate) 220 is stored and retained in the nonvolatile memory 236 to restrict dispersion in detection in the shunt resistance 225 and the current detection circuit 234.

FIG. 3 shows an assembling way of the inverter device, FIG. 4 shows a state of final assembly, and FIGS. 5A and 5B are cross sectional views showing the inverter device.

A case 262 is provided to cover sides of the first substrate 220, and an electric power input terminal block 260 and a motor output terminal block 261 are provided on the case 262. Within the case 262, the first substrate 220 and the second substrate 230 are arranged in this order from a bottom surface in a layered manner. Also, radiating fins for release of heat from the converter 222 a and the inverter 221 a are closely attached to an opposite surface of the bottom to the mounting surface.

In the example shown in FIG. 5A, the first substrate 220 and the second substrate 230 are connected to each other by a lead pin 224, gel 264 is filled on a surface of the first substrate 220 on which the power semiconductor is mounted, and a lid 265 is mounted thereto after the filling of the gel. That is, the second substrate 230 is arranged above the lid 265. Further, the second substrate 230 is structured to be smaller in external form than the case 262.

Also, in the example shown in FIG. 5B, the lid 265 is not provided, the second substrate 230 is arranged to be housed in the case 262, and a resin material 266 is charged from an upper surface of the filled gel 264 to an upper surface of the second substrate 230. Thereby, a waste space can be eliminated as far as mounting of the inverter device in an outdoor unit of an air conditioner, for example, is concerned.

As described above, an electric current output to the electric motor can be grasped by the shunt resistance for over-current protection, mounted on the metallic substrate, so that it is possible to eliminate a current sensor. Accordingly, it is possible to decrease a region, in which a current sensor is mounted, and to make the control substrate small in size. Also, since the shunt resistance is not an additional part, the metallic substrate is not increased in size. Further, since the current detection mechanism (the current detection circuit) mounted on the control substrate is also a necessary part in current detection at the current sensor and not a part added by virtue of current being detected by the shunt resistance, the control substrate is not increased in size. That is, reduction in manhour for the assembly work and reduction in part mount area can be achieved, and by having the shunt resistance for over-current protection of the inverter power semiconductor serving as current detection means for inverter control, current sensors, which are conventionally provided, can be reduced and cost reduction can be achieved.

Also, since the first substrate 220 and the second substrate 230 are compactly arranged close to each other in a layered manner, it is possible to shorten interconnection length in that area, which involves a large possibility of noise generation, that is, to reduce the factor for noise generation.

Further, for a relatively weak communication signal greatly influenced by electromagnetic noise, for example, greatly influenced by the compressor 101 that requires a large electric current, an optical signal is transmitted to the microcomputer 231 via the photo-coupler 243, so that malfunction due to mixing of noise is eliminated and reliability in the refrigerating cycle can be enhanced.

FIG. 6 is a view illustrating current detection means, and FIG. 7 is a view illustrating current reproduction means, which detects an electric current with the shunt resistance and calculates the electric current as sine wave A.C. current being output to the electric motor.

An electric current (D.C. current Idc) flows through the shunt resistance 225 according to the switching action of the switching elements 221. The switching elements are composed of six elements, that is, a U-phase upper arm element, a U-phase lower arm element, a V-phase upper arm element, a V-phase lower arm element, a W-phase upper arm element, and a W-phase lower arm element. Also, the switching action is determined by carrier frequency (triangular wave), and fundamental waves (sine waves) of U-phase, V-phase, and W-phase.

FIG. 6 shows a case where a maximum voltage phase corresponds to U-phase, an intermediate voltage phase corresponds to V-phase, a minimum voltage phase corresponds to W-phase, and a minimum voltage phase current corresponds to a case where the U-phase upper arm element is made ON, the V-phase upper arm element is made ON, and the W-phase lower arm element is made ON, in which case an electric current having flowed through the U-phase upper arm flows to the V-phase upper arm and the W-phase lower arm through the electric motor. Therefore, an electric current Iw of W-phase (minimum voltage phase) will flow through the shunt resistance 225.

Also, a maximum voltage phase current corresponds to a case where the U-phase upper arm element is made ON, the V-phase lower arm element is made ON, and the W-phase lower arm element is made ON, in which case an electric current having flowed through the U-phase upper arm flows to the V-phase lower arm and the W-phase lower arm through the electric motor. Therefore, an electric current Iu of U-phase (maximum voltage phase) will flow through the shunt resistance 225.

FIG. 7 shows flow, in which an electric current is reproduced, such that an electric current (D.C. current Idc) detected by the shunt resistance 225 is amplified by the current detection circuit 234 to be taken into the microcomputer 231.

The microcomputer 231 can grasp which magnitude of electric current flows through which phase, on the basis of a current value (D.C. current Idc) as taken in and information (information about which phases correspond to maximum phase, intermediate phase, and minimum phase and which element or elements are made ON) under PWM (Pulse Width Modulation) control of the microcomputer 231 itself. Therefore, by continuously grasping an electric current, it is possible to grasp (current reproduction) a three-phase sine wave A.C. current being output to the electric motor.

Also, information having contributed to current reproduction is made use of in vector control (control to determine the magnitude and phase of a voltage supplied to the electric motor so that the rotor magnetic flux and the stator current of the electric motor make torque maximum). Accordingly, it is possible to perform control equivalent to inverter control with a current value detected by a current sensor.

A second embodiment of the inverter device according to the invention will be described with reference to FIGS. 8 and 9. FIG. 8 shows a block diagram of a single-phase input inverter device. The inverter device comprises a first substrate (metallic substrate) 220 and a second substrate (control substrate) 230. Mounted on the first substrate 220 are a converter 222 a that serves to convert an A.C. voltage from a single-phase A.C. power supply 251 into a D.C. current, an inverter 221 a (inverter power semiconductor) comprising a D.C./A.C converter, an active circuit 270 a that improves a supply power factor, a shunt resistance 225 that detects a D.C. current flowing through the inverter power semiconductor, and a shunt resistance 272 that detects a D.C. current input from the single-phase A.C. power supply 251. Further, radiating fins made of copper or aluminum are closely attached to an opposite surface to the mount surface. Mounted on the second substrate 230 are a microcomputer 231, a current detection circuit 234 that processes a detection value detected by the shunt resistance 225, an active current detection circuit 274 that processes a detection value detected by the shunt resistance 272, a driver circuit 232 that causes the inverter power semiconductor to perform a switching operation, an active driver circuit 273 that causes an active power semiconductor to perform a switching operation, a communication circuit 241 that communicates with a cycle control substrate 254, and a power circuit 233 that supplies control power to the microcomputer 231, the current detection circuit 234, the active current detection circuit 274, the driver circuit 232, the active driver circuit 273, and the communication circuit 241.

An A.C. voltage from the single-phase A.C. power supply 251 is converted by the converter 222 a (in which a plurality of rectifying devices 222 are bridge-connected) into a D.C. current, the active circuit 270 a (a switching element 270 is arranged between a secondary-side (+) line of a reactor 252 and an output-side (−) line of the converter 222 a) improves a supply power factor, and the inverter 221 a (power conversion means, in which switching elements 221 are three-phase bridge-connected) being a D.C./A.C converter is controlled as A.C. frequency by the microcomputer 231 to drive the electric motor 111.

The A.C. voltage is rectified by the plurality of rectifying devices 222 in the converter 222 a to be conducted to a smoothing capacitor 251 via a magnet switch 253 that operates or stops the compressor 101, the power factor improvement reactor 252, the switching element 270 of the active circuit, and a first recovery element 271.

In the inverter 221 a, flywheel elements 223 are provided in parallel to the switching elements 221 and mounted together on the first substrate 220 in order to regenerate that counter-electromotive force from the electric motor 111, which is generated when the switching elements 221 are switched.

Also, a rush inhibition resistance 244 is provided in parallel to the magnet switch 253 so as to prevent the magnet switch 253, which closes at the time of power-on, from being fused by an excessive rush current that flows through the capacitor 251.

In the inverter 221 a, flywheel elements 223 are provided in juxtaposition with the switching elements 221 and mounted together on the first substrate 220 in order to regenerate that counter-electromotive force from the electric motor 111, which is generated when the switching elements 221 are switched.

An electric current supplied to the electric motor 111 is detected as a D.C. current, which is to flow to the inverter power semiconductor, by the shunt resistance 225, amplified by the current detection circuit 234 to be taken into the microcomputer 231, and reproduced as an A.C. current, which is output to the electric motor, by the microcomputer 231 to be monitored.

An electric current input from the single-phase A.C. power supply 251 is detected as a D.C. current by the active shunt resistance 272, amplified by the active current detection circuit 274 to be taken into the microcomputer 231, and monitored by the microcomputer 231.

The driver circuit 232 is provided between the microcomputer 231 and the switching elements 221 to amplify a weak signal from the microcomputer 231, to a level, in which the switching elements 221 can be driven. Further, the active driver circuit 273 is provided between the microcomputer 231 and the active switching element 270 to amplify a weak signal from the microcomputer 231, to a level, in which the switching elements 270 can be driven.

The communication circuit 241 is composed of an interface connector 242, into which a signal from the cycle control substrate 254 is input, and a photo-coupler 243 that transmits the input signal as an optical signal to the microcomputer 231, and the communication circuit makes transmission and reception in a state, in which electric isolation is established.

A part of a D.C. current generated by the converter 222 a on the first substrate 220 is regulated to a control power of 5 V or 15 V or so from high voltage used in the inverter 221 a, by the power circuit 233 provided on the second substrate 230 to be supplied to the microcomputer 231, the current detection circuit 234, the active current detection circuit 274, the driver circuit 232, the active driver circuit 273, and the communication circuit 241.

By providing a frequency change-over switch 235, capable of changing and fixing the operating frequency of the compressor, on the second substrate (control substrate) 230, it is possible to make performance evaluation on the operating frequency.

A nonvolatile memory is arranged on the second substrate (control substrate) 230, and data of detection gain (an inclination of a straight line that connects a detection value taken into the microcomputer 231 via the current detection circuit 234 when a predetermined electric current is caused to flow through the shunt resistance 225, and a detection value taken into the microcomputer 231 via the current detection circuit 234 when current of 0 ampere is caused to flow through the shunt resistance 225) in the case where the shunt resistance 225 is mounted on the first substrate (metallic substrate) 220 and data of detection gain (an inclination of a straight line that connects a detection value taken into the microcomputer 231 via the active current detection circuit 274 when a predetermined electric current is caused to flow through the active shunt resistance 272, and a detection value taken into the microcomputer 231 via the active current detection circuit 274 when current of 0 ampere is caused to flow through the active shunt resistance 272) in the case where the active shunt resistance 272 is mounted on the first substrate (metallic substrate) 220 are stored and retained in the nonvolatile memory 236 to restrict dispersion in detection in the shunt resistance 225 and the current detection circuit 234 and dispersion in detection in the active shunt resistance 272 and the active current detection circuit 274.

It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. 

1. A refrigerating apparatus having a refrigerating cycle including a compressor driven by an electric motor, of which operating frequency is variably controlled by an inverter device, wherein the inverter device includes a converter circuit that converts an A.C. voltage from an A.C. power supply into a D.C. current, an inverter circuit comprising a D.C./A.C converter, and a shunt resistance that detects a D.C. current flowing through a switching element of the inverter circuit, and a D.C. value detected by the shunt resistance is calculated as a sine wave A.C. current for the electric motor in relation to action of the switching element.
 2. A refrigerating apparatus according to claim 1, wherein the inverter device comprises: a first substrate on a surface of which the shunt resistance is mounted and an opposite surface of which radiating fins are closely attached; a second substrate on which a microcomputer that controls the switching element, a current detection circuit that processes a detection value detected by the shunt resistance, a driver circuit that causes the switching element to perform a switching operation, a connector for communication circuit/interface that communicates with a high-order control substrate, and a power circuit that supplies control power to the microcomputer, the current detection circuit, the driver circuit and the communication circuit are mounted; and a case that covers sides of the first substrate, the case being provided with terminal blocks for electric power input and motor output; wherein the first substrate and the second substrate are arranged in an order of the first substrate and the second substrate in a layered manner from a bottom surface of the case, the first substrate and the second substrate are connected to each other by a lead pin, and gel is filled on a surface of the first substrate on which a power semiconductor is mounted.
 3. A refrigerating apparatus according to claim 2, wherein the operating frequency is output to the high-order control substrate via the connector for interface.
 4. A refrigerating apparatus according to claim 2, wherein refrigerating cycle information (temperature, pressure, opening degrees of expansion valves, rotating speeds of fans) is input into the microcomputer via the connector for interface, and the refrigerating cycle is controlled by the microcomputer.
 5. A refrigerating apparatus according to claim 2, wherein a nonvolatile memory is arranged on the second substrate and data of detection gain of the shunt resistance are stored and retained in the nonvolatile memory.
 6. A refrigerating apparatus according to claim 1, further comprising an active switching element that constitutes an active circuit, and a shunt resistance that detects an electric current of a single-phase power supply input, and a single-phase power supply is input into the converter circuit.
 7. An inverter device that variably controls the operating frequency of an electric motor, the inverter device comprising a converter circuit that converts an A.C. voltage from an A.C. power supply into a D.C. current, an inverter circuit comprising a D.C./A.C converter, and a shunt resistance that detects a D.C. current flowing through a switching element of the inverter circuit, wherein a D.C. value detected by the shunt resistance is calculated as a sine wave A.C. current for the electric motor in relation to action of the switching element.
 8. An inverter device according to claim 7, further comprising: a first substrate on a surface of which the shunt resistance is mounted and on an opposite surface of which radiating fins are closely attached; a second substrate on which a microcomputer that controls the switching element, a current detection circuit that processes a detection value detected by the shunt resistance, a driver circuit that causes the switching element to perform a switching operation, a connector for communication circuit/interface that communicates with a high-order control substrate, and a power circuit that supplies control power to the microcomputer, the current detection circuit, the driver circuit, and the communication circuit are mounted; and a case that covers sides of the first substrate, the case being provided with terminal blocks for electric power input and motor output, wherein the first substrate and the second substrate are arranged in an order of the first substrate and the second substrate in a layered manner from a bottom surface of the case, the first substrate and the second substrate are connected to each other by a lead pin, and gel is filled on a surface of the first substrate on which a power semiconductor is mounted.
 9. An inverter device according to claim 8, wherein a frequency change-over mechanism capable of changing and fixing the operating frequency of the compressor is mounted on the second substrate.
 10. An inverter device according to claim 8, wherein a nonvolatile memory is arranged on the second substrate and data of detection gain of the shunt resistance are stored and retained in the nonvolatile memory.
 11. An inverter device according to claim 7, further comprising an active switching element that constitutes an active circuit, and a shunt resistance that detects an electric current of a single-phase power supply input, and a single-phase power supply is input into the converter circuit. 